In drilling wells for oil and gas exploration, understanding the structure and properties of the associated geological formation provides information to aid such exploration. A number of different measurements in a borehole can be performed to attain this understanding. Further, the usefulness, efficiency, and accuracy of traditional measurements may be related to the precision or quality of the techniques to attain and process data derived from such measurements. Techniques and apparatus to simplify measurements, to enhance processing of measured data, to enhance analysis of data from measurements to provide properties of a formation or a borehole, or to provide combinations thereof can further aid in drilling operations.
In field applications using a scintillation detector coupled to a commercial photodetector, detection systems are designed to maximize their detection efficiency by matching the wavelength of scintillation light to the spectral response curve of a photodetector. A scintillation detector produces light in response to incident radiation. A scintillation detector is herein referred to as a scintillator. In an ideal system, the region of highest intensity in the emission spectrum of the scintillator is aligned to overlap the region of highest quantum efficiency in the spectral response curve of the photodetector. Typically, a decision on the choice of a scintillator is made to meet the goal of specific applications, followed by selection of a photodetector whose spectral response is well matched to the chosen scintillator. However, this matching process is practical only when there is a sufficient number of photodetector devices, such as photomultiplier tubes (PMTs), available from which to choose. However, selection of a PMT in a well logging application is limited to those designed, ruggedized, and manufactured for high temperature environment. Such PMTs, with a high temperature bi-alkali photocathode, show maximum detection efficiency with the incident scintillation light whose wavelength is around 400 nm. Many commercial scintillators of interest in well logging applications show their highest light intensity with much longer wavelengths than 375 nm. These differences in output wavelength of the scintillator and the wavelength response of the photodetector device result in impractical detection efficiency. This problem has been slowing down the use of newer scintillators in well logging applications, because their wavelengths are less optimal to be implemented.